Electro-optically active device

ABSTRACT

An electro-optically active display device including at least one individually addressable pixel, each pixel being provided with an obstructing element, such as a reservoir light shield, a black matrix or a mirror element. A portion of at least one electrical component is positioned beneath the obstructing element in such a way that the portion is not visible for a viewer of the display device.

This application claims the benefit of U.S. patent application Ser. No.10/517,458, filed Dec. 8, 2004.

The present invention relates to an improved electro-optically activedisplay.

An electrophoretic display, being one example of an electro-opticallyactive display where there is physical transport of theelectro-optically active medium through the device, essentiallycomprises a suspension of coloured particles in a liquid having anothercolour than the above particles. The display may be driven in twostates, a distributed state, in which the particles are distributed in adisplay cell in such a way that they essentially cover the cell area,and a collected state, in which the particles are collected in a chosenarea of the cell, in order to affect the transmission of the cell in asmall extent, if any. For the collection of particles, someelectrophoretic displays comprises a reservoir part incorporated in thecell. The reservoir part comprises an obstructing light shield element,behind which the particles may be collected in said collected state, insuch a way that the particles are not visible for a viewer. Thissolution has the drawback that said obstructing light shield elementtakes up a part of the cell area, and thereby limits the transmission ofthe cell, but on the other hand, the remaining active transmission areaof the cell may be totally emptied on particles in the collected state,thereby offering good transmission characteristics in this state.

However, usually an electrophoretic display further comprises of aregular lateral array of electrophoretic cells, said array being drivenby means of active matrix driving. Such active matrix driving requires alarge number of components, which must be placed in each of the pixelcells, making up the display. Examples of such components are spacers,gate and data lines, storage capacitors and TFTs. Since such componentsare placed in the cell, these will occupy a part of the active viewingand transmission area of the cell, thereby limiting the transmission ofthe cell. This is especially the case in electrophoretic transmissive ortransflective displays, in which the electrophoretic layer is switchedby lateral fields.

Hence, a problem with prior art displays is that a comparatively largearea of the cell is occupied with a variety of components as statedabove, which limits the transmission capabilities of the display.

Previously, some attempts have been made to solve the above problem, forexample by making the components as small as possible or by making themessentially transparent, as suggested by U.S. Pat. No. 6,337,761.However, the components may still have a negative effect on thetransmission through the active cell area, and therefore an improveddisplay device, overcoming the above drawback, is desired.

Hence, the object of the present invention is to overcome at least someof the drawbacks with the prior art electrophoretic displays, andprovide a display with improved transmission characteristics.

The above and other objects are achieved by the invention by anelectrophoretic display device, comprising at least one individuallyaddressable pixel, each pixel being provided with an obstructingelement, being characterised in that a portion of at least onecomponent, being one of an electrical or a mechanical component, ispositioned beneath the obstructing element in such a way that theportion is not visible for a viewer of the display device. In this way,the maximum area of an active cell area is available for transmissiveoperation, and hence the transmission of the display device is improved.

Examples of the obstructing element are reservoir light shield, blackmatrix and mirror element.

Preferably, said at least one component is one of a spacer, a barrier agate electrode, a data electrode, a storage capacitor or a thin filmtransistor, which are all components commonly present in currentelectrophoretic displays. However, many other components such as sensorsfor temperature etc. may in accordance with the invention also bepositioned in the same way to achieve the same advantageous effects.

According to a preferred embodiment of this invention, said display is areservoir electrophoretic display device, comprising a reservoir lightshield, beneath which one or more of an electrode, a storage capacitorand a thin film transistor is positioned. In this case, the light shieldis necessarily present in the cell, and by positioning other componentsbeneath said light shield, the active transmission area of the cell maybe maximised. Moreover, said pixel may further comprise a reflectiveelement for enabling transflective operation, whereby a portion of anadditional component, such as a source electrode is positioned beneaththe reflective element, in such a way that it is not visible for aviewer of the display device. By covering source lines with thereflector, the area available for transmission is maximised, in the caseof transflective operation.

This invention will hereinafter be described by means of presentlypreferred embodiments, with reference to accompanying drawings.

FIG. 1 is a plan view of a possible array layout in accordance with thisinvention.

FIG. 2 is schematic cross-section of a reservoir electrophoretic displaydevice in accordance with the invention.

This invention relates to an electrophoretic display device 1, forexample as shown in FIG. 2, comprising a plurality of cells, each cell 2comprising a suspension of charged colored particles in alight-transmissive fluid. Each cell 2 essentially comprises atransmissive front substrate 2, a gate electrode 5A, a source electrode4A and a back substrate, being arranged to be reflective, transmissiveor transflective (FIG. 2 shows a transflective device as an example).The arrangement of these components will be defined below. The cellfurther comprises a light shield element 3 in order to provide areservoir part of the cell. The remaining part of the cell, not beingcovered by the light shield element 3, constitutes an active cell part.The display may be driven in two states, a collected state and adistributed state. In the distributed state, the electrodes 4A, 5A areso driven that the particles of the suspension are distributedthroughout the active cell part, so that light being transmitted throughthe cell in either direction are disturbed by the presence of saidparticles. In the collected state, the electrodes 4A, 5A are so driventhat the charged particles essentially are collected in the reservoirpart of the cell, and thereby do not disturb the transmission of lightthrough the active cell part. In order to achieve the desiredcharacteristics of the light transmission in the distributed state, thepigmentation and coloring the pigments and the light-transmissive fluidmay be adjusted in accordance with prior art.

FIG. 1 is a plan view of one possible embodiment of the invention. FIG.1 discloses a part of an electrophoretic display active matrix array 1,comprising four cells. Each of said cells 2 is associated with a lightshield 3 in order to provide a reservoir part of the cell. The displayfurther comprises a source line 4 as well as a gate line 5. Inaccordance with the invention, the gate line 5 is positioned beneath thelight shield 3, so that it is not visible for a viewer of the display.In this way, the gate line 5 do not occupy any extra space of the activecell part, and hence do not affect the transmission characteristics ofthe display. The source line 4 is in a known manner positionedessentially perpendicular to the gate line 5. Furthermore, the displaycell comprises a TFT 8 (thin film transistor) and a storage capacitor 6,the combination of which is used to apply selected voltages to eachindividual pixel, by means of an addressing scheme as is commonly usedin liquid crystal displays (LCDs) in accordance with prior art. Both theTFT and the storage capacitor are positioned beneath the light shield 3,so that they are not visible for a viewer of the display and hence donot occupy any extra space of the active cell part. By organising theabove components in this way, the maximum area is available fortransmissive operation of the display. The above configuration maymoreover be used in any one of a reflective, transmissive ortransflective display device. In the case or a transflective device, inwhich a part of the back substrate of the cell is provided withreflective element 11, as described above, it is further possible toposition said source line 4 beneath the reflector (i.e. not visible fora viewer of the display element), and thereby maximise the areaavailable for transmission.

The above configuration is especially suitable in transflective andtransmissive electrophoretic displays using a lateral field incombination with the above reservoir function. Since the reservoir is aninactive area of the cell and shields everything in the affected areafrom view, essentially all electrical and mechanical components requiredfor the display should preferably be placed behind said light shielddefining the reservoir, thereby maximizing the transmission. Suchcomponents may for example include gate and source electrodes, TFTs,storage capacitors, spacers, barriers and sensors.

Alternatively, components of the above mentioned kind may be positionedbehind other elements, such as under a black matrix or a mirror element,already present in the display structure.

Although this invention has been described with respect to specificembodiments, the details thereof are not to be construed as limitations,and many variations, modifications and alterations will be apparent fora man skilled in the art, and is intended to be included within thescope of this invention. As a specific example, the invention may notonly be used in electrophoretic displays, but is equally applicable toother electro-optically active displays, which work on the principlethat there is a physical transport of electro-optically active mediumbetween a visible pixel area and a more or less hidden area. Otherexamples of such displays are electro-wetting displays, which utilisesmovement of coloured oil layers, and electro-mechanical displays, whichutilises the movement of for example foils.

1. Electro-optically active display device with physical transport ofthe electro-optically active medium through the device, comprising atleast one individually addressable pixel, each pixel being provided withan obstructing element, wherein a portion of at least one component,being one of an electrical component other than an electrode andelectrode driving lines, is positioned beneath the obstructing elementin such a way that the portion is not visible for a viewer of thedisplay device.
 2. The display device according to claim 1, wherein saidat least one component is one of a storage capacitor, a sensor or a thinfilm transistor.
 3. The display device according to claim 1, whereinsaid display is a reservoir electrophoretic display device, comprising areservoir light shield, beneath which one or more of an electrode, astorage capacitor, a sensor, and a thin film transistor is positioned.4. The display device according to claim 3, said pixel furthercomprising a reflective element for enabling transflective operation,whereby a portion of an additional component is positioned beneath thereflective element, in such a way that the portion of the additionalcomponent is not visible for a viewer of the display device.
 5. Thedisplay device according to claim 1, wherein said display is one of anelectrophoretic display, an electro-wetting display or anelectro-mechanical display.
 6. The display device according to claim 1,wherein a portion of a mechanical component is positioned beneath theobstructing element in such a way that the portion of the mechanicalcomponent is not visible for a viewer of the display device.
 7. Thedisplay device according to claim 6, wherein the mechanical component isat least one of a spacer and a barrier.
 8. The display device accordingto claim 1, wherein the obstructing element is arranged behind a frontsubstrate.
 9. The display device according to claim 1, wherein a portionof a spacer is positioned beneath the obstructing element.
 10. Thedisplay device according to claim 1, wherein a portion of each of atleast two electrical components are positioned beneath the obstructingelement.
 11. The display device according to claim 1, wherein a portionof at least one of a gate line and an electrode is positioned beneaththe obstructing element.
 12. The display device according to claim 1,wherein the at least one component is arranged perpendicular to aviewing direction.
 13. The display device according to claim 1, whereinthe obstructing element is one of a reservoir light shield, a blackmatrix and a reflecting element.
 14. A reservoir electrophoretic displaydevice, comprising at least one individually addressable pixel, saidpixel having a reservoir light shield, said pixel further comprising areflective element for enabling transflective operation, wherein atleast a portion of an electrical component is positioned beneath thereflective element in such a way that the portion is not visible for aviewer of the display device.
 15. The display device according to claim14, wherein the electrical component is one or more of an electrode, astorage capacitor, a sensor, a source line and a thin film transistor.16. The display device according to claim 14, wherein at least a portionof a mechanical component is positioned beneath the reflective elementin such a way that the portion of the mechanical component is notvisible for a viewer of the display device.
 17. The display deviceaccording to claim 14, wherein a portion of at least one of anelectrical or a mechanical component is positioned beneath the reservoirlight shield in such a way that the portion is not visible for a viewerof the display device.
 18. The display device according to claim 17,wherein the portion of the at least one of an electrical or a mechanicalcomponent is a portion of the electrical component and wherein theelectrical component is one or more of an electrode, a storagecapacitor, a sensor, a source line and a thin film transistor.
 19. Thedisplay device according to claim 17, wherein the portion of the atleast one of an electrical or a mechanical component is a portion of themechanical component and wherein the mechanical component is one or moreof a spacer and a barrier.